Hi all,

On Mon, 05 Jan 2026 20:23:36 -0800 Roman Gushchin [off-list ref] wrote:

Alexei Starovoitov [off-list ref] writes:

quoted

On Sun, Jan 4, 2026 at 6:04 PM Stephen Rothwell [off-list ref] wrote:  

quoted

Today's linux-next merge of the bpf-next tree got a semantic conflict in:

  include/linux/memcontrol.h
  mm/memcontrol-v1.c
  mm/memcontrol.c

between commit:

  eb557e10dcac ("memcg: move mem_cgroup_usage memcontrol-v1.c")

from the mm-unstable tree and commit:

  99430ab8b804 ("mm: introduce BPF kfuncs to access memcg statistics and events")

from the bpf-next tree producing this build failure:

mm/memcontrol-v1.c:430:22: error: static declaration of 'mem_cgroup_usage' follows non-static declaration
  430 | static unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap)
      |                      ^~~~~~~~~~~~~~~~
In file included from mm/memcontrol-v1.c:3:
include/linux/memcontrol.h:953:15: note: previous declaration of
'mem_cgroup_usage' with type 'long unsigned int(struct mem_cgroup *,
bool)' {aka 'long unsigned int(struct mem_cgroup *, _Bool)'}
  953 | unsigned long mem_cgroup_usage(struct mem_cgroup *memcg, bool swap);
      |               ^~~~~~~~~~~~~~~~

I fixed it up (I reverted the mm-unstable tree commit) and can carry the
fix as necessary. This is now fixed as far as linux-next is concerned,
but any non trivial conflicts should be mentioned to your upstream
maintainer when your tree is submitted for merging.  You may also want
to consider cooperating with the maintainer of the conflicting tree to
minimise any particularly complex conflicts.  

what's the proper fix here?

Roman,

looks like adding mem_cgroup_usage() to include/linux/memcontrol.h
wasn't really necessary, since kfuncs don't use it anyway?
Should we just remove that line in bpf-next?  

Yep. It was used in the previous version, but not in the latest one.

Just sent an official fix.

And with that now applied to the bpf-next tree, I will no longer revert
the mm-unstable commit.

Thanks.
-- 
Cheers,
Stephen Rothwell